Not every word in English has its plural form written by adding an -s. In fact, English has a lot of important, everyday irregular plural nouns. These are words that have their plural forms built by adopting strategies other than adding the prototypical -s. However, as you’ll see in the list, some plural nouns can be written in two different ways, one that follows the -s pattern, and one that is irregular. Many people get confused when they have to write the plural form of these words. If you are here, though, you won’t be one of them anymore! Here’s a comprehensive list of irregular plural nouns in English.
| addendum | addenda; addendums |
| aircraft | aircraft |
| alumna | alumnae |
| alumnus | alumni |
| analysis | analyses |
| antenna | antennae; antennas |
| antithesis | antitheses |
| apex | apices; apexes |
| appendix | appendices; appendixes (medical context) |
| aquarium | aquaria; aquariums |
| axis | axes |
| bacillus | bacilli |
| bacterium | bacteria |
| basis | bases |
| beau | beaux; beaus |
| bison | bison |
| buffalo | buffalo |
| bureau | bureaux; bureaus |
| cactus | cacti; cactus; cactuses |
| calf | calves |
| château | châteaux; châteaus |
| child | children |
| cod | cod; cods |
| codex | codices |
| concerto | concerti; concertos |
| corpus | corpora |
| crisis | crises |
| criterion | criteria |
| curriculum | curricula; curriculums |
| datum | data |
| deer | deer; deers |
| diagnosis | diagnoses |
| die | dice; dies |
| domino | dominoes; dominos |
| dwarf | dwarves; dwarfs |
| echo | echoes |
| elf | elves |
| ellipsis | ellipses |
| emphasis | emphases |
| erratum | errata |
| faux pas | faux pas |
| phenomenon | phenomena |
| fez | fezzes; fezes |
| fish | fish; fishes |
| focus | foci; focuses |
| foot | feet |
| formula | formulae; formulas |
| fungus | fungi; funguses |
| genus | genera; genuses |
| goose | geese |
| graffito | graffiti |
| grouse | grouse; grouses |
| half | halves |
| hero | heroes |
| hippopotamus | hippopotami; hippopotamuses |
| hoof | hooves; hoofs |
| hypothesis | hypotheses |
| index | indices; indexes |
| iris | irises; irides |
| knife | knives |
| larva | larvae; larvas |
| leaf | leaves |
| libretto | libretti; librettos |
| life | lives |
| loaf | loaves |
| locus | loci |
| louse | lice |
| man | men |
| mango | mangoes |
| matrix | matrices; matrixes |
| medium | media; mediums |
| memorandum | memoranda |
| minutia | minutiae |
| moose | moose |
| motto | mottoes; mottos |
| mouse | mice |
| nebula | nebulae; nebulas |
| nucleus | nuclei; nucleuses |
| oasis | oases |
| octopus | octopi; octopuses |
| offspring | offspring; offsprings |
| opus | opera; opuses |
| ovum | ova |
| ox | oxen |
| parenthesis | parentheses |
| person | persons; people |
| penny | pence; pennies |
| phenomenon | phenomena; phenomenons |
| phylum | phyla |
| plateau | plateaux; plateaus |
| potato | potatoes |
| quiz | quizzes |
| radius | radii; radiuses |
| referendum | referenda; referendums |
| runner-up | runners-up; runner-ups |
| salmon | salmon; salmons |
| scarf | scarves; scarfs |
| self | selves |
| series | series |
| sheaf | sheaves; sheafs |
| sheep | sheep |
| shelf | shelves |
| shrimp | shrimp; shrimps |
| species | species |
| stimulus | stimuli |
| stratum | strata |
| swine | swine |
| syllabus | syllabi; syllabuses |
| symposium | symposia; symposiums |
| synopsis | synopses |
| tableau | tableaux; tableaus |
| thesis | theses |
| thief | thieves |
| tomato | tomatoes |
| tooth | teeth |
| torpedo | torpedoes |
| trout | trout; trouts |
| tuna | tuna; tunas |
| vertebra | vertebrae; vertebras |
| vertex | vertices; vertexes |
| veto | vetoes |
| vita | vitae |
| volcano | volcanoes |
| vortex | vortices; vortexes |
| wharf | wharves; wharfs |
| wife | wives |
| wolf | wolves |
| woman | women |
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